The Animal Maintenance/Bacteriology core is essential for the successful completion of the projects described in this grant proposal. Its functions can be divided into two broad areas. The animal surgery and maintenance section of the core will be responsible for the following activities and services: (1) providing careful control of intravenous feeding regimens or other specialized diets in experimental animals that will be used, namely rats and opossums; (2) providing the means to carefully monitor rats and opossums after performing various surgical procedures; (3) providing the facilities for total parenteral nutrition (intravenous hyperalimentation) of as many as 12 rats of 6 opossums at a time; (4) providing the facilities for small animal surgery; (5) providing the expertise for many different surgical procedures in small animals and the instruction and assistance of fellows and graduate students in these procedures. The bacteriology section of the core will be responsible for the following activities and services: (1) providing the facilities for the performance of complete aerobic and anaerobic bacteriology studies as they relate to the projects proposed in this grant, and (2) providing the expertise for many different microbiological procedures and the instruction and assistance of fellows and graduate students in these procedures. It is anticipated that the projected use of the Animal Maintenance/Bacteriology Core will be as follows: Project I (PI - Frank G. Moody, M.D.) - 35%; Project II (PI - Thomas A. Miller, M.D.) - 40%; Project III (PI - Stuart I. Myers, M.D.) - 10%; Project IV (Gilbert A. Castro, Ph.D.) - 15%.